A method, system, storage medium and device for determining equivalent strength of mudstone

Abstract

This application provides a method, system, storage medium, and device for determining the equivalent strength of mudstone. The method includes: numerically simulating the process of drilling fluid intrusion into mudstone using simulation parameters to obtain the intrusion length and simulated liquid cut of each intrusion zone; calculating the actual intrusion parameters using a mudstone mass algorithm to determine the mass of drilling fluid intrusion into mudstone; calculating the actual liquid cut using an actual liquid cut algorithm to determine the actual liquid cut; fitting the compressive strength of mudstone core and the actual liquid cut to obtain a fitting relationship model; determining the target compressive strength of each intrusion zone based on the fitting relationship model and the simulated liquid cut of each intrusion zone; and determining the equivalent strength of mudstone using an equivalent strength algorithm, the intrusion length of each intrusion zone, and the target compressive strength. This method can accurately determine the change in the equivalent strength of mudstone after drilling fluid intrusion.

Description

Technical Field

[0001] This application relates to the field of oil and gas exploration and development, and more specifically, to a method, system, storage medium, and device for determining the equivalent strength of mudstone. Background Technology

[0002] During drilling, drilling fluid plays a crucial role in maintaining wellbore stability, ensuring wellbore cleanliness, and cooling the drill bit. However, it also faces the challenge of intruding into formations and causing rock strength degradation. When drilling into mudstone formations, the drilling fluid filtrate reacts with clay minerals in the mudstone, altering the mechanical properties of the surrounding rocks and easily leading to wellbore collapse and spalling. On one hand, wellbore collapse and spalling result in irregular well diameters, reducing cementing quality and hindering the efficient development of oil and gas resources in the later stages. On the other hand, severe wellbore collapse and spalling can lead to wellbore instability and collapse, causing stuck pipe or even wellbore abandonment, resulting in huge economic losses.

[0003] Current research on the impact of drilling fluid intrusion on mudstone strength primarily involves measuring the mechanical properties of the rock before and after immersion in drilling fluid, as well as determining the compressive strength of the rock after different immersion times. The overall conclusion is that, compared to water-based drilling fluids, oil-based drilling fluid intrusion causes relatively less degradation in mudstone strength. However, existing experiments evaluating the impact of drilling fluid intrusion on mudstone strength mainly measure the mudstone strength before and after immersion. In these experiments, the drilling fluid intrudes into the core in all directions, while in actual drilling, the drilling fluid only intrudes into the formation radially along the wellbore, exhibiting unidirectional properties. Therefore, the experimentally measured results of rock strength degradation due to drilling fluid differ significantly from actual downhole conditions, making it impossible to objectively evaluate the extent of the impact of drilling fluid intrusion on mudstone strength. Summary of the Invention

[0004] This application aims to provide a method, system, storage medium, and device for determining the equivalent strength of mudstone, with the goal of accurately determining the change in the equivalent strength of mudstone after drilling fluid intrusion.

[0005] The first aspect of this application provides a method for determining the equivalent strength of mudstone, the method comprising: Numerical simulations of the drilling fluid intrusion process into mudstone were conducted using various simulation parameters to obtain the intrusion length and simulated liquid cut of drilling fluid in various intrusion zones within the mudstone during the drilling cycle. Drilling fluid invasion experiments were conducted on mudstone cores to obtain various actual invasion parameters. The mudstone quality algorithm was then used to calculate the mass of drilling fluid invading the mudstone at different invasion time points. The actual liquid content of drilling fluid invading mudstone at different invasion time points is calculated by using the actual liquid content algorithm, thereby determining the actual liquid content of mudstone at different invasion time points. The compressive strength of mudstone cores at different intrusion time points was obtained during uniaxial compressive strength testing of mudstone cores. The compressive strength of mudstone cores at different intrusion time points and the actual liquid content were fitted to obtain a fitting relationship model. Based on the fitted relationship model and the simulated liquid content of each intrusion zone during the drilling cycle, the target compressive strength of each intrusion zone during the drilling cycle is determined. The equivalent strength algorithm is used to calculate the invasion length, target compressive strength and total invasion length of each invasion area during the drilling cycle, and to determine the equivalent strength of mudstone during the drilling cycle.

[0006] Optionally, the process of drilling fluid intrusion into mudstone is numerically simulated using various simulation parameters to obtain the intrusion length and simulated liquid cut of drilling fluid in various intrusion zones within the mudstone during the drilling cycle, including: Numerical simulations of the drilling fluid intrusion process into mudstone were conducted using various simulation parameters to obtain the intrusion range of drilling fluid in mudstone during the drilling cycle and the intrusion fluid content corresponding to each length value within the intrusion range. Determine the target intrusion liquid content that satisfies the preset rules among the intrusion liquid content corresponding to each of the length values; The invasion range is divided into invasion areas based on the length values ​​corresponding to the liquid content of each target invasion, and the invasion length of each invasion area is determined. Based on the determined liquid content of each target intrusion, the simulated liquid content of each intrusion area is determined.

[0007] Optionally, drilling fluid invasion experiments are conducted on mudstone cores to obtain various actual invasion parameters. These parameters are then calculated using a mudstone quality algorithm to determine the mass of drilling fluid invading the mudstone at different invasion time points, including: Drilling fluid invasion experiments were conducted on mudstone cores to obtain various actual invasion parameters; The actual invasion parameters are calculated based on multiple preset invasion time points and mudstone quality algorithms to determine the mass of drilling fluid invading mudstone at different invasion time points. The expression for the mudstone quality algorithm is as follows:

[0008] in, γ is the mass of drilling fluid intruding into mudstone; r is the average pore radius of mudstone; γ is the surface tension of drilling fluid; θ is the wetting angle; μ is the viscosity of drilling fluid; t is the intrusion time point; S is the effective contact area of ​​intrusion; φ is the rock porosity; ρ is the density of drilling fluid.

[0009] Optionally, the actual liquid cut in the mudstone at different invasion time points is calculated using an actual liquid cut algorithm to determine the actual liquid cut in the mudstone at different invasion time points, including: Substitute the mass of drilling fluid invading the mudstone at different invasion time points and the mass of dry rock samples without invading drilling fluid into the actual liquid content algorithm to obtain the actual liquid content in the mudstone at different invasion time points. The algorithm for the actual liquid content is as follows:

[0010] in, Let be the actual liquid content corresponding to the j-th intrusion time point in the mudstone. The quality of the dry rock sample.

[0011] Optionally, the compressive strength and actual liquid content of mudstone cores at different intrusion time points are fitted to obtain a fitting relationship model, including: The compressive strength and actual liquid content of mudstone cores corresponding to multiple different intrusion time points were substituted into the initial relationship model for fitting, and the values ​​of the fitting coefficients were determined. The expression for the initial relational model is:

[0012] in, The compressive strength of the mudstone core corresponding to the j-th intrusion time point; denoted as σ0, where σ0 is the compressive strength of the dry rock sample; α is the fitting coefficient. Based on the values ​​of the fitting coefficients and the initial relationship model, the corresponding fitting relationship model between the target compressive strength and the simulated liquid content is determined. The expression for the fitting relationship model is:

[0013] in, The target compressive strength of the i-th intrusion zone during the drilling cycle; The simulated liquid cut of the i-th intrusion zone during the drilling cycle.

[0014] Optionally, the equivalent strength of the mudstone during the drilling cycle is obtained by calculating the invasion length, target compressive strength, and total invasion length of each invasion zone within the drilling cycle using an equivalent strength algorithm, including: The equivalent strength of mudstone during the drilling cycle is obtained by substituting the invasion length, target compressive strength, and total invasion length of each invasion zone into the equivalent strength algorithm. The expression for the equivalent strength algorithm is:

[0015] In the formula: The equivalent strength of mudstone during the drilling cycle; The length of the i-th intrusion zone within the drilling cycle; This represents the total length of the drilling fluid intrusion into the mudstone.

[0016] Optionally, the method further includes: Obtain the equivalent strength of mudstone over multiple drilling cycles; An equivalent strength diagram representing the dynamic change of mudstone equivalent strength after drilling fluid intrusion is drawn based on the mudstone equivalent strength over multiple drilling cycles. Based on the dynamic trend of the equivalent strength of mudstone in the equivalent strength diagram, the drilling fluid injection scheme in the actual drilling process is determined.

[0017] A second aspect of this application provides a system for determining the equivalent strength of mudstone, applied to any of the methods for determining the equivalent strength of mudstone described in the first aspect, the system comprising: The numerical simulation module is used to numerically simulate the process of drilling fluid invading mudstone using various simulation parameters, and to obtain the intrusion length and simulated liquid content of drilling fluid in various intrusion areas of mudstone during the drilling cycle. The mudstone quality determination module is used to conduct drilling fluid invasion experiments on mudstone cores, obtain various actual invasion parameters, and calculate the quality of drilling fluid invasion into mudstone at different invasion time points using a mudstone quality algorithm. The actual liquid content determination module is used to calculate the mass of drilling fluid invading mudstone at different invasion time points using the actual liquid content algorithm, and to determine the actual liquid content in mudstone at different invasion time points. The fitting relationship model determination module is used to obtain the compressive strength of mudstone cores at different intrusion time points during uniaxial compressive strength testing of mudstone cores, and to fit the compressive strength of mudstone cores at different intrusion time points with the actual liquid content to obtain the fitting relationship model. The target compressive strength determination module is used to determine the target compressive strength of each intrusion zone within the drilling cycle based on the fitted relationship model and the simulated liquid content of each intrusion zone within the drilling cycle. The mudstone equivalent strength determination module is used to determine the mudstone equivalent strength within the drilling cycle by calculating the invasion length, target compressive strength, and total invasion length of each invasion zone within the drilling cycle using an equivalent strength algorithm.

[0018] A third aspect of this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the method for determining the equivalent strength of mudstone as described in any of the first aspects.

[0019] A fourth aspect of this application provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, when the processor executes the computer program, it implements the steps of the method for determining the equivalent strength of mudstone as described in any of the first aspects.

[0020] Beneficial effects: This application provides a method for determining the equivalent strength of mudstone. The method includes: numerically simulating the process of drilling fluid intrusion into mudstone using various simulation parameters to obtain the intrusion length and simulated liquid cut of drilling fluid in each intrusion zone of mudstone during the drilling cycle; conducting drilling fluid intrusion experiments on mudstone cores to obtain various actual intrusion parameters, and calculating the various actual intrusion parameters using a mudstone quality algorithm to determine the mass of drilling fluid intrusion into mudstone at different intrusion time points; and calculating the mass of drilling fluid intrusion into mudstone at different intrusion time points using an actual liquid cut algorithm to determine the mass of non-hydraulic mudstone intrusion. The actual liquid content at the same invasion time point is determined; the compressive strength of mudstone cores at different invasion time points during uniaxial compressive strength testing of mudstone cores is obtained, and the compressive strength of mudstone cores at different invasion time points and the actual liquid content are fitted to obtain a fitting relationship model; based on the fitted relationship model and the simulated liquid content of each invasion area within the drilling cycle, the target compressive strength of each invasion area within the drilling cycle is determined; the invasion length, target compressive strength, and total invasion length of each invasion area within the drilling cycle are calculated using an equivalent strength algorithm to determine the equivalent strength of mudstone within the drilling cycle.

[0021] Numerical simulations were performed on the acquired parameters to obtain the simulated invasion length and simulated liquid cut of each invasion zone in the mudstone after the drilling fluid invaded along the invasion direction. This avoids the problem of drilling fluid invading mudstone in various directions, which is caused by soaking the drilling fluid in existing technologies. Then, by calculating various actual invasion parameters, the mass of drilling fluid invading mudstone at different invasion time points was obtained. Based on the mass of drilling fluid invading mudstone at different invasion times and the mass of the dry rock sample, the actual liquid cut was determined. Based on the actual liquid cut at different invasion time points and the compressive strength of the mudstone core, a fitting relationship model reflecting the relationship between the liquid cut and strength of the mudstone after the drilling fluid invasion was determined, so as to accurately identify the sensitivity of different mudstones to the invasion amount. The simulated liquid cut of each invasion zone was then substituted into the fitting relationship model to obtain the target compressive strength corresponding to each invasion zone. Finally, based on the equivalent strength algorithm, the simulated liquid cut of each invasion zone, and the target compressive strength, the equivalent strength of the mudstone after drilling fluid invasion was accurately determined. The method for determining the equivalent strength of mudstone provided in this application can accurately determine the equivalent strength of mudstone for each drilling cycle after drilling fluid invades mudstone along the direction of invasion into the well wall. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart illustrating a method for determining the equivalent strength of mudstone according to an embodiment of this application; Figure 2 This is a schematic diagram of different intrusion zones in mudstone provided in one embodiment of this application; Figure 3 This is a simulation result diagram of different intrusion zones in mudstone provided in one embodiment of this application; Figure 4 This is a diagram showing the liquid content distribution in mudstone according to an embodiment of this application; Figure 5 This is a schematic diagram of a system for determining the equivalent strength of mudstone according to an embodiment of this application. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] This application provides a method for determining the equivalent strength of mudstone. Furthermore, as... Figure 1 As shown, this application provides a flowchart of a method for determining the equivalent strength of mudstone; specifically, the method includes: S11: Numerical simulation of the drilling fluid intrusion into mudstone is performed using various simulation parameters to obtain the intrusion length and simulated liquid cut of drilling fluid in each intrusion zone of mudstone during the drilling cycle.

[0026] In this embodiment, the simulation parameters refer to the formation properties recorded in the drilling data obtained after drilling is completed, as well as the relevant parameters of the drilling fluid. Specific simulation parameters include: actual formation temperature, pore pressure, drilling fluid density, drilling fluid viscosity, mudstone porosity, and permeability. Based on these various simulation parameters, the process of drilling fluid intrusion into mudstone is numerically simulated to simulate the change in liquid content within the mudstone after the drilling fluid intrudes along the wellbore intrusion direction. With continuous drilling fluid input, the longer the drilling cycle, the greater the amount of drilling fluid input. Since the drilling fluid intrudes into the formation along the wellbore, the liquid content in the formation closer to the wellbore is greater. Therefore, the drilling fluid content varies in different parts of the mudstone depending on the drilling cycle. In this embodiment, a drilling cycle is set, and the change in liquid content within the mudstone during this drilling cycle is simulated. The intrusion length and simulated liquid content of the drilling fluid in each intrusion zone of the mudstone are determined using the micro-element method based on the liquid content within the mudstone.

[0027] Specifically, in this embodiment, the mudstone infiltrated with drilling fluid is divided into multiple intrusion zones based on the fluid content in the formation. Each intrusion zone has its own corresponding intrusion length and simulated fluid content. The intrusion length refers to the length value of each intrusion zone of the mudstone. For example... Figure 2 and Figure 3 As shown, this embodiment also provides a schematic diagram of different intrusion zones in mudstone and a simulation result diagram of different intrusion zones in mudstone. Figure 2 In the diagram, drilling fluid intrudes into the mudstone from left to right, forming an intruded section. This intruded section is then divided into sections based on its fluid content. ... , Invaded area, in Figure 3 In the middle, the liquid content in the intrusion area gradually decreases from left to right.

[0028] S12: Conduct drilling fluid invasion experiments on mudstone cores to obtain various actual invasion parameters, and calculate the quality of drilling fluid invasion into mudstone at different invasion time points using a mudstone quality algorithm.

[0029] Specifically, core samples are drilled from actual mudstone for drilling fluid invasion experiments. During the experiments, various parameters of the mudstone core and drilling fluid are recorded to obtain various actual invasion parameters, such as the average pore radius of the mudstone, drilling fluid surface tension, wetting angle, drilling fluid viscosity, effective contact area of ​​the invasion, rock porosity, and drilling fluid density. Since drilling fluid invasion of the mudstone core is a continuous process, to more accurately monitor the mass change of the mudstone after drilling fluid invasion, this embodiment selects multiple invasion time points to calculate the mass of the mudstone invaded by the drilling fluid. Specifically, the obtained actual invasion parameters and invasion time points are substituted into the mudstone mass algorithm for calculation to obtain the mass of the mudstone invaded by the drilling fluid corresponding to that invasion time point. Multiple invasion time points are substituted into the mudstone mass algorithm to obtain the mass of the mudstone invaded by the drilling fluid corresponding to each invasion time point.

[0030] S13: The actual liquid content of drilling fluid entering the mudstone at different invasion time points is calculated using the actual liquid content algorithm to determine the actual liquid content of the mudstone at different invasion time points.

[0031] Specifically, in order to obtain the actual liquid content in the mudstone at different invasion time points after drilling fluid invasion experiments on mudstone cores, this embodiment substitutes the mass of the mudstone infiltrated by drilling fluid at each invasion time point and the mass of the dry rock sample without drilling fluid infiltration into the actual liquid content algorithm for calculation. The mass of the dry rock sample without drilling fluid infiltration is the mass of the mudstone core drilled from the mudstone.

[0032] S14: Obtain the compressive strength of mudstone cores at different intrusion time points during uniaxial compressive strength testing, and fit the compressive strength of mudstone cores at different intrusion time points with the actual liquid content to obtain a fitting relationship model.

[0033] In this embodiment, uniaxial compressive strength tests were also conducted on the obtained mudstone cores, and the compressive strength of the mudstone cores at different intrusion time points during the test was obtained. This compressive strength refers to the average compressive stress on the cross-section of the mudstone core specimen when it is destroyed under uniaxial pressure, and it reflects the mudstone's resistance to drilling collapse. When drilling fluid intrudes into the mudstone, it enters along fractures and wets the mineral particles in the rock. The addition of liquid alters the physical state of the rock, weakening the bonding force between particles, and thus reducing the rock's compressive strength. Therefore, establishing the relationship between compressive strength and liquid content helps engineers better predict and assess engineering risks, preventing the mudstone's compressive strength from decreasing to the point where it cannot withstand drilling collapse due to excessive drilling fluid input.

[0034] Then, by fitting the compressive strength and actual liquid content of mudstone cores at multiple intrusion time points, a fitting relationship model that reflects the relationship between the compressive strength and liquid content of the mudstone is obtained. Using this fitting relationship model, inputting any liquid content into the model will yield the compressive strength corresponding to that liquid content.

[0035] S15: Based on the fitted relationship model and the simulated liquid content of each intrusion zone during the drilling cycle, determine the target compressive strength of each intrusion zone during the drilling cycle.

[0036] Specifically, since the relationship between mudstone compressive strength and liquid cut can be determined through a fitting model, the simulated liquid cut of each intrusion zone in the mudstone, determined through numerical simulation, is substituted into the fitting model to obtain the target compressive strength corresponding to that simulated liquid cut. This target compressive strength is the predicted compressive strength of the intrusion zone after drilling fluid is injected into the mudstone during the current drilling cycle. Because there are multiple intrusion zones within the mudstone, each with its own corresponding simulated liquid cut, the target compressive strength corresponding to each intrusion zone can be determined through the fitting relationship.

[0037] S16: The equivalent strength of mudstone within the drilling cycle is determined by calculating the invasion length, target compressive strength, and total invasion length of each invasion zone within the drilling cycle using the equivalent strength algorithm.

[0038] Specifically, the equivalent strength of mudstone during the drilling cycle can be obtained by substituting the intrusion length, target compressive strength, and total intrusion length of each intrusion zone into the equivalent strength algorithm. This equivalent strength reflects the overall resistance of mudstone to external forces under the action of drilling fluid. Since the intrusion of drilling fluid may alter the stability of mudstone, making it more susceptible to collapse, rockfall, and other accidents, this reduction in stability is reflected in the equivalent strength. This manifests as a decrease in the overall resistance of mudstone under the action of drilling fluid; that is, a decrease in the equivalent strength of mudstone corresponds to a decrease in its overall resistance to intrusion of drilling fluid.

[0039] In conjunction with the above embodiments, in one implementation, the present invention also provides a method for determining the equivalent strength of mudstone. In this method for determining the equivalent strength of mudstone, step S11 includes steps S21 to S24: S21: Numerical simulation of the drilling fluid intrusion into mudstone is performed using various simulation parameters to obtain the intrusion range of drilling fluid in mudstone during the drilling cycle and the intrusion fluid cut corresponding to each length value within the intrusion range. S22: Determine the target intrusion liquid content that meets the preset rules among the intrusion liquid content corresponding to each of the length values; S23: Divide the invasion range into invasion areas based on the length values ​​corresponding to the liquid content of each target invasion, and determine the invasion length of each invasion area; S24: Based on the determined liquid content of each target intrusion, determine the simulated liquid content of each intrusion area.

[0040] Specifically, numerical simulations of the drilling fluid intrusion process into mudstone are performed using various simulation parameters obtained after drilling is completed. A drilling cycle is selected to obtain the intrusion range of the drilling fluid in the mudstone within that cycle; this intrusion range represents the extent to which the drilling fluid exists in the mudstone. Similarly, the intrusion fluid cut corresponding to various length values ​​within this intrusion range is also obtained during the simulation, such as... Figure 4 As shown in the figure, this embodiment also provides a distribution map of liquid content in mudstone. Figure 4 The drilling cycle was set at 20 days. Various simulation parameters were used to simulate the extent of drilling fluid intrusion into the mudstone during these 20 days, such as... Figure 4 The penetration range is 0-20mm, and each length value within the penetration range has its own corresponding penetration liquid content.

[0041] The system determines whether the liquid content corresponding to each length value meets the target liquid content of a preset rule. This target liquid content is set by the engineer based on the construction situation. For example, the target liquid content can be set to 0%, 0.3%, 0.6%, 0.9%, etc. If the liquid content corresponding to a length value meets the target liquid content of the preset rule, the length value corresponding to that liquid content is determined as the boundary line for the intrusion area, thus determining the intrusion length of each intrusion area within the entire intrusion section. For example, when the liquid content is equal to the target liquid content of 0.3% and 0.6%, the length value of 18mm corresponding to the liquid content of 0.3% is determined as the boundary line for the intrusion area, and the length value of 14mm corresponding to the liquid content of 0.6% is determined as the boundary line for the intrusion area. That is, the intrusion portion between length values ​​of 14mm and 18mm is one intrusion area, and the difference of 4mm between length values ​​of 14mm and 18mm is the intrusion length of that intrusion area.

[0042] In this embodiment, the two target liquid content values ​​used to determine the invasion area are averaged to determine the simulated liquid content of the invasion area. As in the example above, when the target liquid content values ​​of the invasion area are determined to be 0.3% and 0.6%, the average of these two values ​​is 0.45%, which is the simulated liquid content of the invasion area.

[0043] In conjunction with the above embodiments, in one implementation, the present invention also provides a method for determining the equivalent strength of mudstone. In this method for determining the equivalent strength of mudstone, step S12 includes steps S31 to S33: S31: Drilling fluid invasion experiments were conducted on mudstone cores to obtain various actual invasion parameters.

[0044] S32: Calculate the actual invasion parameters based on multiple preset invasion time points and mudstone quality algorithms to determine the quality of drilling fluid invading mudstone at different invasion time points.

[0045] S33: The expression for the mudstone quality algorithm is:

[0046] in, γ is the mass of drilling fluid intruding into mudstone; r is the average pore radius of mudstone; γ is the surface tension of drilling fluid; θ is the wetting angle; μ is the viscosity of drilling fluid; t is the intrusion time point; S is the effective contact area of ​​intrusion; φ is the rock porosity; ρ is the density of drilling fluid.

[0047] After simulating the simulated liquid content of the mudstone, this embodiment also conducted actual physical experiments on the mudstone to determine its mass after drilling fluid intrusion, so as to calculate the actual liquid content of the mudstone using this mass. Specifically, mudstone cores were drilled from the mudstone where the well is located, and drilling fluid intrusion experiments were conducted on these cores. Parameters related to the physical properties of the mudstone and parameters related to the drilling fluid were obtained through these experiments; these parameters are the various actual intrusion parameters. Using the mudstone mass algorithm provided in this embodiment, the mass of the mudstone intruded by drilling fluid at the intrusion time point is calculated based on these various actual intrusion parameters and the intrusion time point. This intrusion time point is any time point selected by the engineer during the drilling fluid intrusion process of the mudstone core, such as 24 hours or 48 hours. The mudstone mass algorithm is as follows:

[0048] Where r is the average pore radius of the mudstone (μm); γ is the surface tension of the drilling fluid (mN / m); θ is the wetting angle (°); μ is the viscosity of the drilling fluid (mPa·s); t is the invasion time (h); S is the effective contact area of ​​the invasion (cm2); φ is the rock porosity (%); and ρ is the density of the drilling fluid (g / cm3). r, γ, θ, μ, S, φ, and ρ are the actual invasion parameters in this embodiment.

[0049] In conjunction with the above embodiments, in one implementation, the present invention also provides a method for determining the equivalent strength of mudstone. In this method for determining the equivalent strength of mudstone, step S13 includes steps S41 to S42: S41: Substitute the mass of drilling fluid invading mudstone at different invasion time points and the mass of dry rock samples without drilling fluid invading into the actual liquid cut algorithm to obtain the actual liquid cut in mudstone at different invasion time points.

[0050] S42: The algorithm for the actual liquid content is as follows:

[0051] in, Let be the actual liquid content corresponding to the j-th intrusion time point in the mudstone. The quality of the dry rock sample.

[0052] Specifically, to determine the liquid content in mudstone after drilling fluid intrusion during the drilling fluid invasion experiment, this embodiment also substitutes the mass of drilling fluid intruding into mudstone and the mass of dry rock samples without drilling fluid intrusion at different invasion time points into the actual liquid content algorithm. This algorithm determines the actual liquid content corresponding to each invasion time point. The actual liquid content algorithm is as follows:

[0053] Let be the actual liquid content corresponding to the j-th intrusion time point in the mudstone. The quality of the dry rock sample.

[0054] In conjunction with the above embodiments, in one implementation, the present invention also provides a method for determining the equivalent strength of mudstone. In this method for determining the equivalent strength of mudstone, step S14 includes steps S51 to S54: S51: Substitute the compressive strength and actual liquid content of mudstone cores corresponding to multiple different intrusion time points into the initial relationship model for fitting, and determine the value of the fitting coefficient.

[0055] S52: The expression for the initial relational model is:

[0056] in, The compressive strength of the mudstone core corresponding to the j-th intrusion time point; denoted as σ, where σ is the compressive strength of the dry rock sample; α is the fitting coefficient.

[0057] Specifically, since the compressive strength of mudstone cores reflects the resistance of mudstone after drilling fluid intrusion, there is a certain relationship between the compressive strength of mudstone cores and the liquid content of mudstone. This embodiment provides a preliminary relationship model to characterize this relationship. The expression of this preliminary relationship model is:

[0058] in, The compressive strength of the mudstone core corresponding to the j-th intrusion time point; denoted as , where is the compressive strength of the dry rock sample; 'a' is the fitting coefficient. By substituting the compressive strength and actual liquid content of mudstone cores corresponding to multiple different intrusion time points into the initial relational model for fitting, the value of the unknown quantity 'a' can be obtained, which is the fitting coefficient in the initial relational model.

[0059] S53: Based on the values ​​of the fitting coefficients and the initial relationship model, determine the corresponding fitting relationship model between the target compressive strength and the simulated liquid content.

[0060] S54: The expression for the fitted relationship model is:

[0061] in, The target compressive strength of the i-th intrusion zone during the drilling cycle; The simulated liquid cut of the i-th intrusion zone during the drilling cycle.

[0062] Specifically, the initial relationship model reflects the relationship between the compressive strength of mudstone and the actual liquid cut in actual mudstone drilling fluid invasion experiments. This relationship also applies to the simulation of mudstone drilling fluid invasion. Therefore, by using the fitting coefficients and the initial relationship model, the correspondence between the simulated liquid cut and the target compressive strength can be determined. Furthermore, since there are multiple invasion zones in the mudstone during the simulation, each invasion zone corresponds to its own simulated liquid cut, and each simulated liquid cut has its own corresponding target compressive strength. This correspondence is represented by a fitting relationship model. The expression of this fitting relationship model is:

[0063] in, The target compressive strength of the i-th intrusion zone during the drilling cycle; The simulated liquid cut of the i-th intrusion zone during the drilling cycle.

[0064] In conjunction with the above embodiments, in one implementation, the present invention also provides a method for determining the equivalent strength of mudstone. In this method for determining the equivalent strength of mudstone, step S16 includes steps S61 to S62: S61: Substitute the invasion length, target compressive strength and total invasion length of each invasion area within the drilling cycle into the equivalent strength algorithm to calculate the equivalent strength of mudstone within the drilling cycle; S62: The expression for the equivalent strength algorithm is:

[0065] In the formula: The equivalent strength of mudstone during the drilling cycle; The length of the i-th intrusion zone within the drilling cycle; This represents the total length of the drilling fluid intrusion into the mudstone.

[0066] Specifically, by substituting the target compressive strength corresponding to each intrusion area obtained through step S15 above, along with the intrusion length of each intrusion area and the total intrusion length within the drilling cycle, into the equivalent strength algorithm, the equivalent strength of the intruded portion of the mudstone within the drilling cycle can be obtained. This equivalent strength is also the simulated resistance capacity of the mudstone within the drilling cycle. The total intrusion length is the sum of the intrusion lengths of all intrusion areas. The expression for this equivalent strength algorithm is:

[0067] In the formula: The equivalent strength of mudstone during the drilling cycle; The length of the i-th intrusion zone within the drilling cycle; This represents the total length of the drilling fluid intrusion into the mudstone.

[0068] In conjunction with the above embodiments, in one implementation, the present invention also provides a method for determining the equivalent strength of mudstone. In this method for determining the equivalent strength of mudstone, the method further includes steps S71 to S73: S71: Obtain the equivalent strength of mudstone over multiple drilling cycles; S72: Based on the equivalent strength of mudstone over multiple drilling cycles, draw an equivalent strength diagram representing the dynamic change of the equivalent strength of mudstone after drilling fluid intrusion. S73: Based on the dynamic change trend of the mudstone equivalent strength in the equivalent strength diagram, determine the drilling fluid injection scheme in the actual drilling process.

[0069] In this embodiment, the equivalent strength of mudstone for multiple drilling cycles was also obtained through the above steps. The selection of the drilling cycle is determined by the engineer based on the actual well conditions, and can be 15 days, 20 days, or 25 days. By integrating the obtained equivalent strengths of mudstone within multiple drilling cycles and plotting them on the same equivalent strength map, the equivalent strength in this map changes with the time of the drilling cycle. Therefore, this equivalent strength map reflects the dynamic change law of the equivalent strength of mudstone after drilling fluid intrusion. Through the dynamic change trend of the equivalent strength of mudstone in this equivalent strength map, the drilling fluid injection scheme summarized in the actual drilling process can be further determined. Specifically, since the equivalent strength in this equivalent strength diagram is determined by the simulated liquid cut and invasion length, it is also a simulated diagram of the change in mudstone strength over time after drilling fluid invades the mudstone. The greater the equivalent strength, the stronger the mudstone's resistance to collapse; the smaller the equivalent strength, the weaker the resistance. Based on the change in equivalent strength in the equivalent strength diagram, engineers select the appropriate drilling cycle corresponding to the equivalent strength and determine the corresponding drilling fluid injection volume based on the drilling cycle, thus determining the optimal drilling fluid injection scheme.

[0070] Furthermore, to better explain the above embodiments, this application also provides some examples for illustration: Based on the drilling data and drilling fluid parameters obtained after drilling was completed, the simulation parameters were determined as follows: actual formation temperature 120℃, pore pressure 47MPa, drilling fluid density 1.7g / cm3, drilling fluid viscosity 50mPa·s, mudstone porosity 16%, permeability 0.03mD, and a drilling cycle of 20 days was selected. The mudstone intrusion range and corresponding intrusion liquid content were obtained through numerical simulation. The intrusion area was divided according to the intrusion liquid content, and the length of each intrusion area was calculated. The results are shown in Table 1.

[0071] Table 1. Intrusion length and simulated liquid content of each intrusion zone.

[0072] Drilling fluid invasion experiments were conducted on mudstone. Based on the actual pore radius of 0.01 μm, drilling fluid surface tension of 21 mN / m, wetting angle of 20.75°, drilling fluid viscosity of 50 mPa·s, effective contact area of ​​4.908 cm², porosity of 16%, and drilling fluid density of 1.7 g / cm³, the invasion mass of the drilling fluid at invasion times of 12 h, 24 h, 48 h, 120 h, and 240 h was calculated, as shown in Table 2.

[0073] Table 2 Drilling fluid intrusion quality at different intrusion time points

[0074] The liquid content of mudstone under different intrusion states of drilling fluid was calculated, and the results are shown in Table 3.

[0075] Table 3 Actual liquid content at different intrusion time points

[0076] Uniaxial compressive strength tests were conducted to obtain the compressive strength of mudstone cores under different actual liquid contents. The results are shown in Table 4.

[0077] Table 4 Actual liquid content and corresponding compressive strength

[0078] The liquid cut of 0 corresponds to the control group in this example, i.e., when no drilling fluid is introduced into the mudstone, the compressive strength of the mudstone is calculated. The relationship between liquid cut and compressive strength is fitted using the uniaxial compressive strength test results as follows:

[0079] Based on the above simulation results and the fitted relationship model, the target compressive strength corresponding to each intrusion area was calculated, as shown in Table 5.

[0080] Table 5. Length of each intrusion zone, simulated liquid content, and target compressive strength.

[0081] Based on the target compressive strength corresponding to each core intrusion area, the equivalent strength of the mudstone along the intrusion direction after 20 days was calculated to be 52.27 MPa using the equivalent strength algorithm.

[0082] Based on the same inventive concept, one embodiment of this application provides a system for determining the equivalent strength of mudstone, such as... Figure 5 This is a schematic diagram of a system for determining the equivalent strength of mudstone provided in this embodiment. The system includes: The numerical simulation module is used to numerically simulate the process of drilling fluid invading mudstone using various simulation parameters, and to obtain the intrusion length and simulated liquid content of drilling fluid in various intrusion areas of mudstone during the drilling cycle. The mudstone quality determination module is used to conduct drilling fluid invasion experiments on mudstone cores, obtain various actual invasion parameters, and calculate the quality of drilling fluid invasion into mudstone at different invasion time points using a mudstone quality algorithm. The actual liquid content determination module is used to calculate the mass of drilling fluid invading mudstone at different invasion time points using the actual liquid content algorithm, and to determine the actual liquid content in mudstone at different invasion time points. The fitting relationship model determination module is used to obtain the compressive strength of mudstone cores at different intrusion time points during uniaxial compressive strength testing of mudstone cores, and to fit the compressive strength of mudstone cores at different intrusion time points with the actual liquid content to obtain the fitting relationship model. The target compressive strength determination module is used to determine the target compressive strength of each intrusion zone within the drilling cycle based on the fitted relationship model and the simulated liquid content of each intrusion zone within the drilling cycle. The mudstone equivalent strength determination module is used to determine the mudstone equivalent strength within the drilling cycle by calculating the invasion length, target compressive strength, and total invasion length of each invasion zone within the drilling cycle using an equivalent strength algorithm.

[0083] Based on the same inventive concept, another embodiment of this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the method for determining the equivalent strength of mudstone as described in any of the above embodiments.

[0084] Based on the same inventive concept, another embodiment of this application provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the method for determining the equivalent strength of mudstone as described in any of the above embodiments.

[0085] In the method for determining the equivalent strength of mudstone provided in this application embodiment, the method uses simulation parameters to numerically simulate the penetration of drilling fluid into mudstone along the wellbore intrusion direction, making the simulated liquid cut more closely resemble the actual liquid cut generated by drilling fluid penetration into mudstone in actual production. The method also uses physical experiments on mudstone cores to obtain a relationship model between liquid cut and compressive strength, enabling targeted calculation of target compressive strength for mudstone. This means different relationship models exist for different types of mudstone, resulting in a more realistic target compressive strength. Furthermore, the method obtains the equivalent strength for each drilling cycle, allowing engineers to determine a more optimal drilling cycle corresponding to the equivalent strength based on the changes in equivalent strength across multiple drilling cycles. This further determines the amount of drilling fluid injected for that cycle, thus determining the drilling fluid injection scheme for mudstone in actual production.

[0086] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0087] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0088] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0089] Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes that element.

[0090] The above provides a detailed description of the method, system, storage medium, and device for determining the equivalent strength of mudstone provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for determining the equivalent strength of mudstone, characterized in that, The method includes: Numerical simulations of the drilling fluid intrusion process into mudstone were conducted using various simulation parameters to obtain the intrusion length and simulated liquid cut of drilling fluid in various intrusion zones within the mudstone during the drilling cycle. Drilling fluid invasion experiments were conducted on mudstone cores to obtain various actual invasion parameters. The mudstone quality algorithm was then used to calculate the mass of drilling fluid invading the mudstone at different invasion time points. The actual liquid content of drilling fluid invading mudstone at different invasion time points is calculated by using the actual liquid content algorithm, thereby determining the actual liquid content of mudstone at different invasion time points. The compressive strength of mudstone cores at different intrusion time points was obtained during uniaxial compressive strength testing of mudstone cores. The compressive strength of mudstone cores at different intrusion time points and the actual liquid content were fitted to obtain a fitting relationship model. Based on the fitted relationship model and the simulated liquid content of each intrusion zone during the drilling cycle, the target compressive strength of each intrusion zone during the drilling cycle is determined. The equivalent strength algorithm is used to calculate the invasion length, target compressive strength and total invasion length of each invasion area during the drilling cycle, and to determine the equivalent strength of mudstone during the drilling cycle.

2. The method for determining the equivalent strength of mudstone according to claim 1, characterized in that, Numerical simulations of drilling fluid intrusion into mudstone were conducted using various simulation parameters to obtain the intrusion length and simulated fluid cut of drilling fluid in different intrusion zones within the mudstone during the drilling cycle, including: Numerical simulations of the drilling fluid intrusion process into mudstone were conducted using various simulation parameters to obtain the intrusion range of drilling fluid in mudstone during the drilling cycle and the intrusion fluid content corresponding to each length value within the intrusion range. Determine the target intrusion liquid content that satisfies the preset rules among the intrusion liquid content corresponding to each of the length values; The invasion range is divided into invasion areas based on the length values ​​corresponding to the liquid content of each target invasion, and the invasion length of each invasion area is determined. Based on the determined liquid content of each target intrusion, the simulated liquid content of each intrusion area is determined.

3. The method for determining the equivalent strength of mudstone according to claim 1, characterized in that, Drilling fluid invasion experiments were conducted on mudstone cores to obtain various actual invasion parameters. These parameters were then calculated using a mudstone quality algorithm to determine the mass of drilling fluid invading the mudstone at different invasion time points, including: Drilling fluid invasion experiments were conducted on mudstone cores to obtain various actual invasion parameters; The actual invasion parameters are calculated based on multiple preset invasion time points and mudstone quality algorithms to determine the mass of drilling fluid invading mudstone at different invasion time points. The expression for the mudstone quality algorithm is: in, γ is the mass of drilling fluid intruding into mudstone; r is the average pore radius of mudstone; γ is the surface tension of drilling fluid; θ is the wetting angle; μ is the viscosity of drilling fluid; t is the intrusion time point; S is the effective contact area of ​​intrusion; φ is the rock porosity; ρ is the density of drilling fluid.

4. The method for determining the equivalent strength of mudstone according to claim 1, characterized in that, The actual liquid content of drilling fluid invading mudstone at different invasion time points is calculated using an actual liquid content algorithm to determine the actual liquid content in the mudstone at different invasion time points, including: Substitute the mass of drilling fluid invading the mudstone at different invasion time points and the mass of dry rock samples without invading drilling fluid into the actual liquid content algorithm to obtain the actual liquid content in the mudstone at different invasion time points. The algorithm for the actual liquid content is as follows: in, Let be the actual liquid content corresponding to the j-th intrusion time point in the mudstone. The quality of the dry rock sample.

5. The method for determining the equivalent strength of mudstone according to claim 1, characterized in that, The compressive strength and actual liquid content of mudstone cores at different intrusion time points were fitted to obtain a fitting relationship model, including: The compressive strength and actual liquid content of mudstone cores corresponding to multiple different intrusion time points were substituted into the initial relationship model for fitting, and the values ​​of the fitting coefficients were determined. The expression for the initial relational model is: in, The compressive strength of the mudstone core corresponding to the j-th intrusion time point; denoted as σ0, where σ0 is the compressive strength of the dry rock sample; α is the fitting coefficient. Based on the values ​​of the fitting coefficients and the initial relationship model, the corresponding fitting relationship model between the target compressive strength and the simulated liquid content is determined. The expression for the fitting relationship model is: in, The target compressive strength of the i-th intrusion zone during the drilling cycle; The simulated liquid cut of the i-th intrusion zone during the drilling cycle.

6. The method for determining the equivalent strength of mudstone according to claim 1, characterized in that, The equivalent strength of the mudstone during the drilling cycle is obtained by calculating the invasion length, target compressive strength, and total invasion length of each invasion zone using an equivalent strength algorithm. This includes: The equivalent strength of mudstone during the drilling cycle is obtained by substituting the invasion length, target compressive strength, and total invasion length of each invasion zone into the equivalent strength algorithm. The expression for the equivalent strength algorithm is: In the formula: The equivalent strength of mudstone during the drilling cycle; The length of the i-th intrusion zone within the drilling cycle; This represents the total length of the drilling fluid intrusion into the mudstone.

7. The method for determining the equivalent strength of mudstone according to claim 1, characterized in that, The method further includes: Obtain the equivalent strength of mudstone over multiple drilling cycles; An equivalent strength diagram representing the dynamic change of mudstone equivalent strength after drilling fluid intrusion is drawn based on the mudstone equivalent strength over multiple drilling cycles. Based on the dynamic trend of the equivalent strength of mudstone in the equivalent strength diagram, the drilling fluid injection scheme in the actual drilling process is determined.

8. A system for determining the equivalent strength of mudstone, applied to the method for determining the equivalent strength of mudstone as described in any one of claims 1-7, characterized in that, The system includes: The numerical simulation module is used to numerically simulate the process of drilling fluid invading mudstone using various simulation parameters, and to obtain the intrusion length and simulated liquid content of drilling fluid in various intrusion areas of mudstone during the drilling cycle. The mudstone quality determination module is used to conduct drilling fluid invasion experiments on mudstone cores, obtain various actual invasion parameters, and calculate the quality of drilling fluid invasion into mudstone at different invasion time points using a mudstone quality algorithm. The actual liquid content determination module is used to calculate the mass of drilling fluid invading mudstone at different invasion time points using the actual liquid content algorithm, and to determine the actual liquid content in mudstone at different invasion time points. The fitting relationship model determination module is used to obtain the compressive strength of mudstone cores at different intrusion time points during uniaxial compressive strength testing of mudstone cores, and to fit the compressive strength of mudstone cores at different intrusion time points with the actual liquid content to obtain the fitting relationship model. The target compressive strength determination module is used to determine the target compressive strength of each intrusion zone within the drilling cycle based on the fitted relationship model and the simulated liquid content of each intrusion zone within the drilling cycle. The mudstone equivalent strength determination module is used to determine the mudstone equivalent strength within the drilling cycle by calculating the invasion length, target compressive strength, and total invasion length of each invasion zone within the drilling cycle using an equivalent strength algorithm.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps in the method for determining the equivalent strength of mudstone as described in any one of claims 1 to 7.

10. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method for determining the equivalent strength of mudstone as described in any one of claims 1 to 7.

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